A number of properties which can withstand use under severe conditions, such as gas shielding (gas barrier) properties, flexibility, transparency, heat resistance, solvent resistance, and interlaminar adhesion are required of substrates in the field of electronic devices for displays, lighting, solar batteries, circuit boards and the like.
For this reason, only substrates of inorganic materials such as Si wafers and glass could have hitherto been used as the substrate for electronic devices. However, substrates of light, cracking-free, and bendable polymer materials (hereinafter referred to as “polymer substrate”) have been desired for meeting recent demands for a weight reduction in products, improved flexibility of substrates, a cost reduction, improved handleability and the like. To this end, studies have been made on the use of synthetic resin sheets or synthetic resin films instead of glass substrates which have been used for constituting conventional displays. In particular, for display applications for organic ELs and film liquid crystals, clear and heat-resistant polymer substrates have been desired. Polymer substrates, however, generally have much larger gas permeability than substrates formed of inorganic materials such as glass. Therefore, in electronic devices using a polymer substrate, since a necessary degree of vacuum within electronic devices cannot be maintained, such electronic devices are disadvantageous, for example, in that gas is passed through the polymer substrate and enters the electronic device, and diffused oxygen oxidizes and deteriorates the device. Accordingly, regarding the prevention of the entry of external oxygen and water vapor, an ultrahigh level of barrier properties has been desired for prolonging the service life of displays.
Thus, gas barrier clear films usable in polymer substrates, which have excellent gas barrier properties, have light weight, are free from cracking, are bendable, and overall properties suitable as an alternative to glass substrates, should meet a number of strict property requirements such as flexibility, transparency, heat resistance, solvent resistance, and interlaminar adhesion, particularly water vapor, oxygen and other gas barrier properties.
Clear resin films have hitherto been known as a substrate of organic electroluminescent elements (see, for example, Japanese Patent Laid-Open Nos. 251429/1990 and 124785/1994). In these organic EL elements, however, the organic film is disadvantageously deteriorated by oxygen and water vapor which enter the organic EL element through a clear resin film. This disadvantageously leads to problems such as unsatisfactory luminescence characteristics and unreliable durability. That is, any highly gas barrier clear resin film, which has satisfactory gas barrier properties in the field of electronic devices such as displays and can ensure good quality of gas barrier objects by virtue of the satisfactory gas barrier properties, has not been developed.
To overcome the above problems, a method for forming a gas barrier layer on a clear heat-resistant base material by sputtering has been proposed (see, for example, Japanese Patent Laid-Open No. 222508/1999). As described in the working examples of the publication, however, the gas barrier level achieved by this method is as low as about 1 cm3/m2 in terms of oxygen permeability.
Further, interposition of an adhesive layer has been proposed in order to improve the adhesion between the resin film and the gas barrier layer (see, for example, Japanese Patent Laid-Open No. 109314/1997). This proposal, however, does not take into consideration the suppression of pinholes in the gas barrier layer derived from protrusions present on the surface of the resin film. Therefore, according to the results of the working examples in this publication, the water vapor permeability is 0.1 g/m2, indicating that the gas barrier properties of this film are still disadvantageously unsatisfactory for use as a gas barrier film in electronic device applications.
Furthermore, a method is also known in which one or more polymerizable monomers in addition to a silane compound component are emulsion polymerized in water to prepare a water dispersed polymer which is used as a gas barrier layer (see, for example, Japanese Patent Laid-Open Nos. 3206/1995 and 18221/1995). In these publications, however, although there is a description on the suppression of oxygen permeability, they do not refer to specific numerical values of the water vapor permeability.